This week, many families will take advantage of the holiday to take their children to the Rose Science Center at the American Museum of Natural History, to the Hall of Science in Queens, or to the Liberty Science Center in Jersey City. Those children whose parents lack the income or the education to take them to science museums will fall even further behind in their knowledge of science.

All of our city’s children need to understand the principles of science, which are so important to their futures and to the future of our nation. Ignorance of science is inexcusable in an age when computer science, medicine, pharmaceuticals, and other technology-related fields are our most dynamic growth-sectors. Yet the latest test administered by the federal government’s National Assessment of Educational Progress shows that our city’s children are at risk of scientific illiteracy.

Last week, the agency released the results of its 2005 science test for students in fourth-grade and eighth-grade in 10 cities, including New York City. The scores reported for big-city students, as compared to the rest of the nation, are deplorable. The performance of New York City students on this exam was especially disappointing. Starting in 2002, when the first national tests in reading and mathematics were offered to big-city districts, New York City scored near the top in those subjects. In 2005, when science was tested for the first time, however, New York City rated only fifth out of the 10 cities.

New Yorkers learned very little from journalists about the performance of our schools on this important federal science test. The New York Times ran a long, two-column article that referred only briefly to the city’s scores, while the New York Post printed a short article accompanied by a misleading graphic that showed New York handily outpacing two of the lowest-scoring cities, Los Angeles and Atlanta.

Nationally, 34% of students in fourth-grade and 43% of those in eighth-grade scored “below basic,” which is the lowest possible ranking. However, in big-city public school districts, 52% of fourth-graders and 61% of eighth-graders were “below basic.” In New York City, 54% of fourth-graders and 64% of eighth-graders were “below basic.”

New York City’s science scores were abysmal, especially in light of the fact that four of the five cities that scored below New York — Cleveland, Atlanta, Chicago, and Los Angeles — have long been known for poor educational performance. Boston may have reason to be even more embarrassed. Just weeks ago, Boston won the coveted Broad Prize for having the nation’s most improved urban schools. But it turns out that 58% of Boston’s fourth-graders and 62% of its eighth-graders were “below basic” in science.

As bad as the overall scores are for New York City, they are even worse when they are broken down by race and ethnicity. Two-thirds of black and Hispanic fourth-grade students were “below basic” on the federal test, as were 77% of black students and 73% of Hispanic students in the eighth-grade. This is a recipe for disaster. Black and Hispanic students are not learning much science in our city’s schools. These students are not being adequately prepared for college or for the modern workplace or for informed citizenship.

The news for white students in the city’s public schools is not much better. In fourth-grade, 27% were “below basic,” and in eighth-grade, 39% were in that category. In both cases, white students in New York City performed significantly below white students in other big-city public school districts.

The low scores of white students explain the relatively small performance gap, compared to other big cities, between different racial groups, about which the city’s Department of Education has boasted. The achievement gap is smaller not because minority students are doing well in the city, but because white students are doing so poorly.

If one were to ask what percentage of students in eighth-grade are really doing well in science in the city’s public schools, the news is bleak. Only 29% of white and Asian students scored proficient or advanced, as did a mere 6% of black students, 7% of Hispanic students, and 9% of low-income students.

None of this should come as a surprise. Two years ago, Eva Moskowitz, who was then chairwoman of the City Council Education Committee, held hearings and issued a report on the shameful state of science education in the New York City public schools. She pointed out that the city school system was failing in its duty to educate students in science, as evidenced by the fact that half the students in fourth- and eighth-grades failed the state science exams.

The Moskowitz report, called “Lost in Space: Science Education in New York City Schools,” concluded that the public school system lacked skilled science teachers, a coherent science curriculum, and adequate facilities. It found that science was virtually absent in elementary schools, where there were few qualified science teachers. In most elementary schools, students were lucky if they received 45 minutes of science instruction once a week. Furthermore, in these grades, there was no curriculum for science, so teachers had no idea what they were expected to teach. Some lessons were repeated, while others were omitted altogether.

In middle schools and high schools, the failure rates on state science tests — like the “below basic” rates on the federal test — were far higher in schools attended by children in poor neighborhoods. Many schools had inadequate laboratory facilities.

In the past two years, nothing has changed to lift the status of science education. The city Department of Education has focused relentlessly on reading and mathematics because these are the subjects that matter most, for they are tested most frequently by the state.

But it is time to recognize that reading and math, important as they are, do not represent a complete education. An education that ignores science, history, the arts, and foreign language is not a worthy education.

Despite the fact that Mayor Bloomberg has added $3.5 billion to the budget of the Department of Education during his time in office, the results for this investment have been meager. While state testing for reading showed an incredible jump in 2005, the 2006 round of state testing for reading showed that achievement has flattened out. Moreover, unlike the state tests, federal reading tests found no gains for the city’s students between 2003 and 2005.

Students are not progressing because the department is committed solely to test scores and not to learning. The relentless pursuit of higher scores has led to a heavy investment in test preparation activities, at the cost of a sound education. Students are spending endless hours practicing to take tests and taking tests, but are not gaining the knowledge, vocabulary, and understanding that come from the study of science and history and other neglected subjects.

In response to the disastrous federal scores in science, the Department of Education has pledged to test science with greater frequency. But that is not the answer to the deficiencies that the federal test — and the Moskowitz report of 2004 — identified. The city schools should have an explicit, coherent, sequential science curriculum that begins in kindergarten and continues every year until high school graduation. And the city must do whatever is necessary to recruit and train highly qualified science teachers so that every student has access to science education.

Tests can tell us where we need to improve instruction and focus our energies. But tests are no substitute for a coherent curriculum and well-prepared teachers.

Ms. Ravitch is research professor of education at New York University and a senior fellow at the Hoover Institution and the Brookings Institution.